DERRY, N.H. — What was once flippantly deemed the Summer of Trump has evolved into something much bigger: a singular moment in American political and cultural history.

That New York businessman Donald Trump would even run for president — much less attract double the support of his nearest GOP rival, former Florida governor Jeb Bush — has struck many Republicans as surreal and likely short-lived. But after seven weeks as the Republican front-runner, historians say, Trump has earned a place in the annals of American politics.

More than 30,000 people have signed up to see Trump at his “pep rally” in Alabama on Friday evening, marking the largest crowd yet for a presidential primary campaign this year. It remains unclear whether Trump will remain the GOP front-runner for president or become this cycle’s version of third-party presidential gadfly.

Either way, Trump’s candidacy will be a moment that today’s voters will have to explain to their grandchildren.

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“What is happening with Trump is not a fluke,” said Harvard government and sociology professor Theda Skocpol, author of “The Tea Party and the Remaking of Republican Conservatism.” “Yes, he is a great entertainer, but he is able to take advantage of a number of dynamics in American politics as they exist right now. This is an important moment.”

Trump is the personification of a 21st-century America fascinated by the super rich and obsessed with celebrity, political historians said in interviews. In politics, his assets provide massive available financing in a national race where money plays an unprecedented role. A hyper-fast media environment means Trump’s candid comments and jaw-dropping insults, such as his jab at US Senator John McCain’s respected military service, permeate Facebook feeds, quickly making him the most-discussed candidate in the field, according to social media analytics.

In addition to demographic changes such as Latino population growth, polling shows an underlying anxiety from a shrinking middle class over pocket-book issues. To gauge the reach of Trump’s words, look no further than Dorchester, where police said two brothers from South Boston attacked a 58-year-old homeless man Wednesday because he was Hispanic. One of the men said he was inspired by Trump, allegedly telling police, “Donald Trump was right, all of these illegals need to be deported.”

Trump’s comments, like calling some illegal immigrants rapists and murderers, offend many. But his message — a promise to “Make America Great Again!” — is resonating, judging by his position in the polls and the throngs of people who come to see him. When he talks about building a secure fence along the Mexican border — an edifice he hopes they will someday call “The Trump Wall” — the crowds cheer him.

When he took to the stage Wednesday night in New Hampshire in front of a raucous audience of nearly 1,000 people, Trump declared that “the silent majority is back,” borrowing a line from Richard Nixon’s winning 1968 presidential campaign. Nixon used that term to describe the majority of Americans who do not publicly express their political opinions.

Earlier, when asked by reporters about the state of the Republican presidential race, he said his Republican rivals in polls are “going up and down like yo-yos. But I’ve been up there for a long time, and I hope I’m going to be up there for a long time.”

Keith Bedford/Globe Staff

Supporters of Donald Trump clamored to take photos of him as he left a town hall meeting in Derry, N.H., on Wednesday.

“The only thing constant is Trump,” he told the press.

Polls show Trump leading the Republican field nationally as well as in the early presidential nominating states of Iowa and New Hampshire. A CNN/ORC poll released last week showed Trump with an 11-percentage-point lead over former Florida governor Jeb Bush, who many Republicans considered to be the front-runner earlier this year. In New Hampshire, a recent survey showed Trump leading Bush by 5 percentage points.

Also in the CNN poll, Trump trails the Democratic front-runner, Hillary Rodham Clinton, by 6 points among registered voters in a hypothetical national matchup. (Other recent polling shows Clinton with double-digit leads over Trump in the swing states of Ohio, Florida, and Pennsylvania.)

More problematic for Trump: 59 percent of respondents in the CNN poll said they have an unfavorable view of him. That might be a problem for him if he is the nominee — or even if he isn’t. Trump has suggested that he could run as a third-party candidate if he does not win the GOP nomination.

Daniel T. Rodgers, a historian at Princeton University, said future historians will probably view Trump as one in a long line of third-party candidates. But, he added, Trump is different from past third-party candidates like socialist Eugene V. Debs in 1912, segregationist George Wallace in 1968, deficit-fighter Ross Perot in 1992, or consumer advocate Ralph Nader in 2000.

Trump can dig deep into his own wealth to fund his campaign, and his candidacy does not revolve around a single issue, Rodgers said.

“We will know if he succeeds as a cultural phenomenon if we see some sort of immigration act pass with his type of vision,” said Rodgers. “But he is clearly less committed to issues than other third-party type candidates have been to theirs.”

Others see Trump among many populist politicians who use showmanship to appeal to middle America’s anxiety, much like former Louisiana governor Huey Long, who tapped into that unease during the Great Depression. Long was assassinated in 1935, a month after launching his presidential bid.

Richard D. White, who wrote “Kingfish: The Reign of Huey P. Long,” says he sees several similarities between Long and Trump.

“[Long] spoke so directly to the people, and that is Donald Trump’s appeal. It is a purely personal relationship with his listeners. It is not based on factual issues,” said White, who also noted similarities in how both candidates dress in flamboyant suits and use fiery rhetoric toward minorities. “The oversimplification of issues is very dangerous and when you combine that with negativity and fear, the combination is classic populism.”

Who knows how long Trump will continue to dominate polls and headlines, but this moment is important, according to Jill Lepore, an American history professor at Harvard University.

“If Trump dropped out of the race tomorrow, his run — his intense appeal, even if it turns out to have been brief — would still be worth reckoning with, as a matter of history,” said Lepore.

James Pindell can be reached at james.pindell@globe.com. Follow him on Twitter @jamespindell, or subscribe to his daily e-mail update on the 2016 campaign at bostonglobe.com/groundgame.